It has been possible to convert the wind's linear motion to circular motion for hundreds of years. However, the prior art machines have not been proved entirely satisfactory. For example, all the known types had to be large and bulky in size to deliver commercially acceptable quantities of energy, wich apart from the expense of making such machines is one of the principal reasons why the aforementioned prior machines have not come more extensively into general use. Another disadvantage of the prior art machines has been the inadequacy to deliver the maximum energy available at various wind velocities. One such prior machine equipped with variable pitch vanes to reduce the impact surface pitch at higher wind velocities, other machines of the class have various type mechanical braking means, or means to reduce the impact surface area to desired level, at the expense of controlling rotation speed. Another disadvantage of prior art machines has been the small surface area utilized in conversion of the wind's energy in comparison to the size of such machines and space needed for operation.